Open bite after a motorcycle collision
A 27-year-old man is brought to a provincial hospital emergency department 6 hours after a motorcycle collision. He has a laceration over the chin, a 3-mm anterior open bite that was not present before the accident, and cannot bring his back teeth together. Mouth opening is 18 mm. There is a step deformity and mobility at the left mandibular parasymphysis; the right temporomandibular joint area is tender, and there is a small laceration in the right external auditory canal. He has no loss of consciousness, no dyspnoea and no cervical spine pain. Tooth 33 is displaced lingually, 34 is mobile, and 38 is partially erupted and lies in the fracture line on the left. The hospital has a panoramic radiograph machine, a CT scanner that is unavailable at night, and an on-call anaesthetist. No rigid fixation plates are in stock; arch bars and wires are available, as is amoxicillin-clavulanate.
1. Which fractures does this patient have, and what is the mechanical explanation for the anterior open bite?
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Fractures: (1) left parasymphysis - mobile segment, step deformity, displaced 33; (2) right condylar/subcondylar fracture - suggested by the TMJ tenderness, the 18 mm opening and the laceration of the external auditory canal, which is a classic sign of a condyle driven backwards.
Why the anterior open bite appears. The parasymphysis fracture lets each posterior fragment rotate upwards under the masseter, medial pterygoid and temporalis, while the anterior fragment is pulled down and back by the suprahyoids and digastric. The posterior teeth therefore contact first and the anterior teeth cannot close. In addition, the loss of ramus height from the right condylar fracture allows further premature posterior contact on that side. The result is an anterior open bite in centric relation - a fracture sign, not a malocclusion.
Key point: a condylar fracture can produce a contralateral open bite, and a parasymphysis fracture combined with a contralateral condylar fracture is the classic pattern. Both sides must be treated as one functional unit. Fixing the symphysis alone without accounting for the condyle leaves the open bite behind.
2. Set out your immediate and definitive management priorities in the order you would carry them out, explaining the reasoning for each.
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Immediate (first hour).
- Primary survey: airway, breathing, circulation. An anterior open bite plus a chin laceration means a mandibular fracture until proved otherwise; do not be distracted by the laceration. No dyspnoea or loss of consciousness here, so no immediate airway intervention.
- Secondary injuries: examine the external auditory canal but do not syringe it; test cranial nerves V and VII and the cervical spine before any manipulation.
- Wound care: analgesia, tetanus prophylaxis, irrigation and temporary closure of the chin laceration.
- Antibiotics: start amoxicillin-clavulanate now - this is a compound fracture because a tooth-bearing segment communicates with the mouth. Do not wait until plating.
Definitive (within 24–72 hours).
- Imaging: panoramic radiograph plus reverse Towne's view; request CT for the morning, since it is unavailable at night and is the standard for condylar assessment.
- Restore occlusion first, then bone. With no plates, apply arch bars and place temporary maxillomandibular fixation to re-establish occlusion, then decide between continued closed treatment (4–6 weeks of MMF with elastics, with early mobilization of the condyle) and referral for open reduction. In this setting, closed management of both fractures is defensible, accepting slightly less precise reduction.
- Supportive care: nutrition, oral hygiene, analgesia, and a scheduled plan for wire and elastic checks. Warn the patient that the occlusion, not the radiograph, is the measure of success.
3. How would you manage tooth 33 and tooth 38? Give the reasoning behind each decision.
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Tooth 38 (partially erupted, in the fracture line). Argue both ways. Retaining it risks infection tracking along the fracture, prevents a tight reduction, and the tooth is functionless and likely to be lost anyway. Extracting it creates a socket communicating with the fracture, may convert a closed fracture into an infected one, and risks displacing a root into the gap. The usual rule in an angle fracture is: remove a badly involved, non-functional, partially erupted or diseased third molar if the fracture can then be reduced and the socket managed; retain a functional, periodontally sound tooth that is only minimally involved, with antibiotics and review.
For this 38 - partially erupted and in the fracture line with no function - most units would remove it at fixation, curette the socket, close primarily and continue antibiotics. If you retain it, document that decision and review at 1, 2 and 4 weeks; a symptomatic tooth in the line then needs removal.
Tooth 33 (displaced lingually). A lingually displaced incisor adjacent to a parasymphysis fracture is usually following its bony segment, so do not extract it reflexively. Reduce the segment and see whether 33 returns to the arch. If it remains mobile and blocks reduction, stabilize it with a wire or remove it. Record vitality at baseline and at 6–8 weeks: a luxated tooth in a fracture line often loses vitality and will need root canal treatment, but not on the day of injury.